I finally got down the temporary floor in the GH after having to remove all the mulch because it started growing mold, mildew and other stuff, and my friend Master Electrician Betsy installed power into it as well .. two outlets on separate circuits.

I need some ideas and advice on how to set up the heating system. What I'm using are 2 forced fan, Milk House Heaters on portable thermostats along with an oscillating fan and static fan.

What I'm wondering, where to place the heaters and fans. I need to decide on what I'm going to do before I start loading the stuff that will be on the ground.

I use the portable milk house heaters with the built in fans.They are round, so the fan's put out warm air 360º. I put them right in the middle aisle. I don't usually have to run the heat during the day here, so it's easy to pick up and move to the side while I'm working in the greenhouse.

The system I have worked perfectly in the 8 foot greenhouses .. this one being 16 feet, I'm thinking I need two fans .. how big is your gh mj?

2 10 x 12's. If we get really cold I have 2 Oil heaters ( electric) that I can add. The fans from the milk house heater's circulate the air. I keep one house min. temp of 55º and the other 50º. I may have to upgrade that next winter. We are planning on renovating one greenhouse to make it taller so I have more sidewall area. Was supposed to do that this year but a complete bathroom in the house got in the way.

I use one heat dish on a thermostat on the floor of my 10 x 12 GH. It radiates heat and doesn't blow. It will turn off if it gets knocked over. I keep the fan on low to help keep the heat from staying up in the ceiling as it rises. It is by Presto bought a Costco. It really puts out the heat!

@ShadyGreenThumb do you find much fluctuation in the temperature? Last year I bought one of those "oil" heaters (has oil inside that heats up) - it fluctuates 4-6 degrees before it warms again. No fan so similar to the Presto in that regard - mine kind of looks like an old-fashioned radiator. It has worked pretty good - but I've got an eye out for something that might be a little more "even" heating - wish it has a thermostat !

You can get a portable thermostat. That's what I use with my milk house heater. They're awesome!

http://www.kkontrols.com/

I have a portable thermostat for the heater set this year at 55º. Last year it was 65º. We'll see how the new insulation works whether I should raise it or not. It is too soon to tell. The box fan is above and to the rear of the heat dish. When the hot air rises as it naturally does, the idea is to get the fan to whirl warm around. I am sure it cools down by the time it rises 8 feet and swirls around. But my thermometer stays constant. The heat dish is closest to a large pot of spiral ginger and Giant BOP, verrrrry tropical plants. I hope it keeps it's soil warm. I have two thermometers, one on the door that I can read from the house. And the one in the center of the GH. For the most part, unless the sun is out, they are the same temperature. And I don't worry about temps when the sun is out.

I have had some trouble keeping the GH temp uniform. I have 3 smaller fans running 24/7, but still see a top vent open and find the heat is also on. The top vent is controlled by a Bayliss auto vent, and the 20k propane heater has it's own power free thermostat that can be set down to 60*F.
I took a small turbo type fan and put it on the floor pointing straight up in the middle of the aisle and seems to have helped a lot to help keep the air from standing from hot on top to cold on bottom. I haven't seen the heat on with the vent open, and the vent seems to be open less.

I finally decided on one milkhouse heater and a box fan .. the box fan is at the top of the greenhouse and the heater just a bit off the ground. I have my thermostat set at 49 degrees with a wireless thermometer hanging from the ceiling and one a foot off the ground. System seems to work well. So far the gh hasn't gotten below 48 degrees. The real test will be when we get into the twenties for extended periods. If I need to I can add another heater and thermostat.